Everyday hiking and walking, as in the sort I might do after work or on the weekend, requires little or no planning. Obviously it’s important to make sure storms aren’t imminent, or trails aren’t closed for some reason, but beyond that, it’s easy just to pick up and go.
Trip planning is different – somewhat. Certainly I treat it differently, in that I take care to note which trails are “must do,” which look like nice backups, and so on. But in some ways, it ends up being similar to everyday experiences due to such factors as unexpected weather and individual whims.